The rheological properties of asphalt have led to its widespread use as the binder in asphalt cement concrete (ACC). Even though asphalt cement concrete has a long history as a useful binder, it has severe performance deficiencies including rutting in hot climates and cracking in cold climates. Modified asphalt binders, especially those containing polymer or crumb rubber, improve high and low temperature Theological properties of asphalt cement concrete. The present invention relates to a method for improving both the high and low temperature performance of asphalt cement binders and mixes containing true binders. The improvements affected were accomplished by developing a unique dispersion system and stabilization technique involving the combination of dispersion and activating agents as well as systematic and well-controlled mixing of the agents and asphalt.
Homogeneous crumb rubber modified asphalts are known in the art, as evidenced by the Memon patent U.S Pat. No. 5,704,971. As disclosed therein, peroxide is mixed with crumb rubber to modify it so that it mixes more evenly with the asphalt. While the peroxide-modified crumb rubber operates satisfactorily, there is still room for improvement of the modified crumb rubber so that it disperses more evenly through the asphalt.
Since crumb rubber is generated by cutting and slicing used tires, any developments which enhance the use of crumb rubber as a supplement to an asphalt composition will significantly improve the environment by reducing stockpiles of tires. The asphalt/crumb rubber composition also has an improved performance in all types of climates. The present invention was developed to improve the crumb rubber modified asphalt with a new treatment process to enhance dispersion of crumb rubber throughout an asphalt composition.
Accordingly, it is a primary object of the present invention to provide a method for making a modified asphalt wherein a dispersion agent such as furfural or vegetable oil is added to a modifier material such as granular crumb rubber or a polymer to form a treated modifier material. This material is mixed at an elevated temperature of between 90xc2x0 C. and 1500xc2x0 C. to ensure that the modifier material is fully treated with the dispersion agent. Next, the treated modifier material is added to hot asphalt, and the combination is mixed. After mixing, a first activator is added to the modified asphalt to produce a devulcanized and stabilized asphalt mixture having improved rheological, separation, and solubility characteristics. A trace amount of micro activator is also added to the modified asphalt to increase the ductility or stretching property of the modified asphalt.
According to a more specific object of the invention, the first activator material comprises an acid such as a Lewis acid and contains a trace of sulfur. The micro activator is phenyl formaldehyde resin.